1. Field of the Invention
The present invention relates to a failure diagnosing circuit and method capable of carrying out failure diagnosis of switching elements constituting a bridge circuit that drives a motor.
2. Description of Related Art
A check circuit for testing a bridge circuit connected to a direct current power source via resistors is described in Japanese Unexamined Utility Model Publication No. Sho 62-198897.
This check circuit is provided with a circuit in which switches are connected in series with the direct current power source and high impedance elements are connected in parallel with the switches. A voltage drop between the high impedance elements is detected when the switches are opened.
This conventional check circuit has several disadvantages. According to this check circuit, each of the switching elements constituting the bridge circuit cannot be individually subjected to failure diagnosis. Further, open failure and a shortcircuit failure of each of the switching elements cannot be detected.